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Abstract

Background—The origin of 40% of syncope cases remains unknown even after a complete diagnostic work-up. Previous studies have suggested that adenosine 5'-triphosphate (ATP) testing has value in selecting successful therapy. This patient-blinded, multicenter, randomized superiority trial tested whether, in patients with syncope of unknown origin (SUO), selecting cardiac pacing in those with a positive ATP test results in fewer recurrences than those who do not receive pacing.

Methods and Results—From 2000 to 2005, 80 consenting patients (mean age 75.9 ± 7.7 years, 81% women, and 56% without diagnosed structural heart disease) with SUO and atrioventricular or sinoatrial block lasting longer than 10 seconds (average 17.9 ± 6.8 seconds) under ATP administration (20 mg IV bolus) were recruited from 10 hospitals, implanted with programmable pacemakers, and randomized to either active pacing (dual-chamber pacing at 70 beats per minute [bpm]) or backup pacing (atrial pacing at 30 bpm). Patients were followed regularly for up to five years for any syncope recurrence, the primary outcome. Mean follow-up was 16 months. Syncope recurred in eight (21%) of 39 patients randomized to active pacing and in 27 (66%) of 41 randomized to backup pacing (control), yielding a hazard ratio of 0.25 (95% CI: 0.12, 0.56). After recurrence, the 27 recurrent control patients were reprogrammed to active pacing and only one reported subsequent syncope.